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Viral Hemorrhagic Fevers

What are viral hemorrhagic fevers?

Viral hemorrhagic fevers (VHF) is a term that refers to a group of illnesses caused by several distinct families of viruses. While some types of hemorrhagic fever viruses cause illnesses that are relatively mild, many of these cause severe, life-threatening diseases with no known cures. Perhaps the most known of this group of diseases is the Ebola virus, made famous by the movie "Outbreak."

Hemorrhagic fever viruses are caused by viruses of four distinct families:

arenaviruses

filoviruses

bunyviruses

flaviviruses

These viruses share the following common features:

The viruses are geographically restricted to the areas where the host species live.

Their survival depends on an animal or insect host, called the natural reservoir.

Humans are not the natural reservoir for any of these viruses; they only become infected when coming into contact with an infected host. However, with some of these viruses, humans can transmit the virus to one another after the accidental transmission from the host.

They are all RNA viruses, covered in a fatty (lipid) coating.

With a few exceptions, there is no known cure or drug treatment for these diseases.

Human outbreaks or cases of these diseases occur sporadically and irregularly, making outbreaks difficult to predict.

What are the natural reservoirs of viral hemorrhagic fevers?

For the most part, rodents and arthropods are the reservoirs for these viruses. Some examples of the rodents involved include the multimammate rat, cotton rat, deer mouse, house mouse, and other field rodents. Arthropod ticks and mosquitoes are vectors for some of the illnesses. However, the hosts of viruses such as the Ebola and Marburg remain unknown.

Where have cases of viral hemorrhagic fever occurred?

The viruses that cause these illnesses are distributed globally. However, since each virus is generally associated with one or more particular host species, the virus and its ensuing disease are usually seen where the host species lives. For some species, this is a limited geographic area; however, in other cases, a particular species may be distributed worldwide.

While people usually become infected only in areas where the host lives, occasionally the host is exported from its natural habitat, causing an outbreak in a different area. Occasionally, an infected person travels from an area where the virus occurs naturally, and if it is the type of virus that can be transmitted by person-to-person contact, others then contract the disease (as was the case with the Ebola hemorrhagic fever). With more and more people traveling each year, outbreaks of these diseases are becoming a greater threat to areas where the diseases have not been seen before.

The Centers for Disease Control and Prevention (CDC) reported a large outbreak of Rift Valley fever early in 1998 in Kenya and Somalia. An outbreak occurred in southwestern Saudi Arabia and Yemen in 2000. The virus is transmitted primarily by infected mosquitoes and other biting insects and occasionally by contact with the blood or body fluids of infected animals.

Travelers are advised to take appropriate precautions to prevent infection. This includes:

liberal use of insect repellent.

wearing long sleeves and pants.

using bednets in areas where outbreaks are occurring.

avoiding contact with livestock in areas where outbreaks are occurring.

Consult your physician for more information.

What are the symptoms of viral hemorrhagic fever diseases?

The specific symptoms of viral hemorrhagic fever diseases vary by the specific disease, and each individual may experience symptoms differently. Initial signs and symptoms often include:

marked fever

fatigue

dizziness

muscle aches

loss of strength

exhaustion

Patients with severe cases often show signs of bleeding under the skin, in internal organs, or from body orifices, such as the mouth, eyes, or ears. While bleeding may occur from many sites around the body, blood loss is rarely the cause of death. Severely ill patients may also experience shock, seizures, nervous system failure, coma, and delirium. Some forms of the viral hemorrhagic fever disease are associated with kidney failure.

The symptoms of viral hemorrhagic fever may resemble other medical conditions or problems. Always consult your physician for a diagnosis.

Treatment for viral hemorrhagic fever:

While patients receive supportive treatment, generally there is no known cure or treatment for these illnesses. The anti-viral drug, ribavirin, has been effective in treating some persons with Lassa Fever and hemorrhagic fever with renal syndrome.

How can viral hemorrhagic fever diseases be prevented?

Because no vaccines exist that can prevent these diseases (with the exception of yellow fever and Argentine hemorrhagic fever), efforts are concentrated on avoiding contact with host species.